Tag Archives: Milky Way

Astronomers Detect Protective Shield Defending Pair of ‘Dwarf Galaxies’ with help of FUSE, Hubble

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For billions of years, the Milky Way’s largest satellite galaxies – the Large and Small Magellanic Clouds – have followed a perilous journey. Orbiting one another as they are pulled in toward our home galaxy, they have begun to unravel, leaving behind trails of gaseous debris. And yet – to the puzzlement of astronomers – these dwarf galaxies remain intact, with ongoing vigorous star formation.

“A lot of people were struggling to explain how these streams of material could be there,” said Dhanesh Krishnarao, assistant professor at Colorado College. “If this gas was removed from these galaxies, how are they still forming stars?”

With the help of data from NASA’s Hubble Space Telescope and a retired satellite called the Far Ultraviolet Spectroscopic Explorer (FUSE), a team of astronomers led by Krishnarao has finally found the answer: the Magellanic system is surrounded by a corona, a protective shield of hot supercharged gas. This cocoons the two galaxies, preventing their gas supplies from being siphoned off by the Milky Way, and therefore allowing them to continue forming new stars.

Description of the above image:

Researchers have used spectroscopic observations of ultraviolet light from quasars to detect and map out the Magellanic Corona, a diffuse halo of hot, supercharged gas surrounding the Small and Large Magellanic Clouds. Shown here in purple, the corona stretches more than 100,000 light-years from the main mass of stars, gas, and dust that make up the Magellanic Clouds, intermingling with the hotter and more extensive corona that surrounds the Milky Way. The Magellanic Clouds, dwarf galaxies roughly 160,000 light-years from Earth, are the largest of the Milky Way’s satellites and are thought to be on their first in-falling passage around the Milky Way. This journey has begun to unravel what were once barred spirals with multiple arms into more irregular-shaped galaxies with long tails of debris. The corona is thought to act as a buffer protecting the dwarf galaxies’ vital star-forming gas from the gravitational pull of the much larger Milky Way. The detection of the Magellanic Corona was made by analyzing patterns in ultraviolet light from 28 distant background quasars. As the quasar light passes through the corona, certain wavelengths (colors) of ultraviolet light are absorbed. The quasar spectra become imprinted with the distinct signatures of carbon, oxygen, and silicon ions that make up the corona gas. Because each quasar probes a different part of the corona, the research team was also able to show that the amount of gas decreases with distance from the center of the Large Magellanic Cloud. This study used archival observations of quasars from Hubble’s Cosmic Origins Spectrograph (COS) and the Far Ultraviolet Spectroscopic Explorer (FUSE). Quasars have also been used to probe the Magellanic Stream, outflows from the Milky Way , and the halo surrounding the Andromeda Galaxy./Illustration Credits: STScI, Leah Hustak

 

This discovery, which was just published in Nature, addresses a novel aspect of galaxy evolution. “Galaxies envelope themselves in gaseous cocoons, which act as defensive shields against other galaxies,” said co-investigator Andrew Fox of the Space Telescope Science Institute in Baltimore, Maryland.

Astronomers predicted the corona’s existence several years ago. “We discovered that if we included a corona in the simulations of the Magellanic Clouds falling onto the Milky Way, we could explain the mass of extracted gas for the first time,” explained Elena D’Onghia, a co-investigator at the University of Wisconsin–Madison. “We knew that the Large Magellanic Cloud should be massive enough to have a corona.”

But although the corona stretches more than 100,000 light-years from the Magellanic clouds and covers a huge portion of the southern sky, it is effectively invisible. Mapping it out required scouring through 30 years of archived data for suitable measurements.

Researchers think that a galaxy’s corona is a remnant of the primordial cloud of gas that collapsed to form the galaxy billions of years ago. Although coronas have been seen around more distant dwarf galaxies, astronomers had never before been able to probe one in as much detail as this.

There’re lots of predictions from computer simulations about what they should look like, how they should interact over billions of years, but observationally we can’t really test most of them because dwarf galaxies are typically just too hard to detect,” said Krishnarao. Because they are right on our doorstep, the Magellanic Clouds provide an ideal opportunity to study how dwarf galaxies interact and evolve.

In search of direct evidence of the Magellanic Corona, the team combed through the Hubble and FUSE archives for ultraviolet observations of quasars located billions of light-years behind it. Quasars are the extremely bright cores of galaxies harboring massive active black holes. The team reasoned that although the corona would be too dim to see on its own, it should be visible as a sort of fog obscuring and absorbing distinct patterns of bright light from quasars in the background. Hubble observations of quasars were used in the past to map the corona surrounding the Andromeda galaxy.

By analyzing patterns in ultraviolet light from 28 quasars, the team was able to detect and characterize the material surrounding the Large Magellanic Cloud and confirm that the corona exists. As predicted, the quasar spectra are imprinted with the distinct signatures of carbon, oxygen, and silicon that make up the halo of hot plasma that surrounds the galaxy.

The ability to detect the corona required extremely detailed ultraviolet spectra. “The resolution of Hubble and FUSE were crucial for this study,” explained Krishnarao. “The corona gas is so diffuse, it’s barely even there.” In addition, it is mixed with other gases, including the streams pulled from the Magellanic Clouds and material originating in the Milky Way.

By mapping the results, the team also discovered that the amount of gas decreases with distance from the center of the Large Magellanic Cloud. “It’s a perfect telltale signature that this corona is really there,” said Krishnarao. “It really is cocooning the galaxy and protecting it.”

How can such a thin shroud of gas protect a galaxy from destruction?

“Anything that tries to pass into the galaxy has to pass through this material first, so it can absorb some of that impact,” explained Krishnarao. “In addition, the corona is the first material that can be extracted. While giving up a little bit of the corona, you’re protecting the gas that’s inside of the galaxy itself and able to form new stars.”

NASA’s Hubble finds spiraling stars ‘NGC 346’, providing window into early universe

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Nature likes spirals – from the whirlpool of a hurricane, to pinwheel-shaped protoplanetary disks around newborn stars, to the vast realms of spiral galaxies across our universe.

Now astronomers are bemused to find young stars that are spiraling into the center of a massive cluster of stars in the Small Magellanic Cloud, a satellite galaxy of the Milky Way.

The outer arm of the spiral in this huge, oddly shaped stellar nursery called NGC 346 may be feeding star formation in a river-like motion of gas and stars. This is an efficient way to fuel star birth, researchers say.

The Small Magellanic Cloud has a simpler chemical composition than the Milky Way, making it similar to the galaxies found in the younger universe, when heavier elements were more scarce. Because of this, the stars in the Small Magellanic Cloud burn hotter and so run out of their fuel faster than in our Milky Way.

Though a proxy for the early universe, at 200,000 light-years away the Small Magellanic Cloud is also one of our closest galactic neighbors.

The massive star cluster NGC 346, located in the Small Magellanic Cloud, has long intrigued astronomers with its unusual shape. This shape is partly due to stars and gas spiraling into the center of this cluster in a river-like motion.
ILLUSTRATION: NASA, ESA, Andi James (STScI)

Learning how stars form in the Small Magellanic Cloud offers a new twist on how a firestorm of star birth may have occurred early in the universe’s history, when it was undergoing a “baby boom” about 2 to 3 billion years after the big bang (the universe is now 13.8 billion years old).

The new results find that the process of star formation there is similar to that in our own Milky Way.

Only 150 light-years in diameter, NGC 346 boasts the mass of 50,000 Suns. Its intriguing shape and rapid star formation rate has puzzled astronomers. It took the combined power of NASA’s Hubble Space Telescope and the European Southern Observatory’s Very Large Telescope (VLT) to unravel the behavior of this mysterious-looking stellar nesting ground.

“Stars are the machines that sculpt the universe. We would not have life without stars, and yet we don’t fully understand how they form,” explained study leader Elena Sabbi of the Space Telescope Science Institute in Baltimore. “We have several models that make predictions, and some of these predictions are contradictory. We want to determine what is regulating the process of star formation, because these are the laws that we need to also understand what we see in the early universe.”

Researchers determined the motion of the stars in NGC 346 in two different ways. Using Hubble, Sabbi and her team measured the changes of the stars’ positions over 11 years. The stars in this region are moving at an average velocity of 2,000 miles per hour, which means that in 11 years they move 200 million miles. This is about 2 times the distance between the Sun and the Earth.

Tarantula Nebula star-forming region in a new light, including tens of thousands of never-before-seen young stars that were previously shrouded in cosmic dust./Photo:NASA, ESA, CSA, STScI, Webb ERO Production Team

But this cluster is relatively far away, inside a neighboring galaxy. This means the amount of observed motion is very small and therefore difficult to measure. These extraordinarily precise observations were possible only because of Hubble’s exquisite resolution and high sensitivity. Also, Hubble’s three-decade-long history of observations provides a baseline for astronomers to follow minute celestial motions over time.

The second team, led by Peter Zeidler of AURA/STScI for the European Space Agency, used the ground-based VLT’s Multi Unit Spectroscopic Explorer (MUSE) instrument to measure radial velocity, which determines whether an object is approaching or receding from an observer.

“What was really amazing is that we used two completely different methods with different facilities and basically came to the same conclusion, independent of each other,” said Zeidler. “With Hubble, you can see the stars, but with MUSE we can also see the gas motion in the third dimension, and it confirms the theory that everything is spiraling inwards.”

But why a spiral?

“A spiral is really the good, natural way to feed star formation from the outside toward the center of the cluster,” explained Zeidler. “It’s the most efficient way that stars and gas fueling more star formation can move towards the center.”

Half of the Hubble data for this study of NGC 346 is archival. The first observations were taken 11 years ago. They were recently repeated to trace the motion of the stars over time. Given the telescope’s longevity, the Hubble data archive now contains more than 32 years of astronomical data powering unprecedented, long-term studies.

“The Hubble archive is really a gold mine,” said Sabbi. “There are so many interesting star-forming regions that Hubble has observed over the years. Given that Hubble is performing so well, we can actually repeat these observations. This can really advance our understanding of star formation.”

Observations with NASA’s James Webb Space Telescope should be able to resolve lower-mass stars in the cluster, giving a more holistic view of the region. Over Webb’s lifespan, astronomers will be able to repeat this experiment and measure the motion of the low-mass stars. They could then compare the high-mass stars and the low-mass stars to finally learn the full extent of the dynamics of this nursery.

The Hubble Space Telescope is a project of international cooperation between NASA and ESA. NASA’s Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy, in Washington, D.C.

30 Doradus: Thousands of stunning young stars in “cosmic tarantula”captured by James Webb telescope

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Thousands of never-before-seen young stars spotted in a stellar nursery called 30 Doradus, captured by NASA’s James Webb Space Telescope, called Tarantula Nebula owing to its appearance in dusty filaments.

The nebula has long been a favorite for astronomers studying star formation and the  Webb has been revealing beautiful distant background galaxies, as well as the detailed structure and composition of the nebula’s gas and dust ever since it’s started capturing the deep space.

At only 161,000 light-years away in the Large Magellanic Cloud galaxy, the Tarantula Nebula is the largest and brightest star-forming region in the Local Group, the galaxies nearest our Milky Way. It is home to the hottest, most massive stars known. Astronomers focused three of Webb’s high-resolution infrared instruments on the Tarantula. Under the lens of Webb’s Near-Infrared Camera (NIRCam), the region resembles a burrowing tarantula’s home, lined with its silk.

The nebula’s cavity centered in the image above has been hollowed out by blistering radiation from a cluster of massive young stars, which sparkle pale blue in the image. Only the densest surrounding areas of the nebula resist erosion by these stars’ powerful stellar winds, forming pillars that appear to point back toward the cluster. These pillars contain forming protostars, which will eventually emerge from their dusty cocoons and take their turn shaping the nebula.

Caption: Nestled in the center of the Tarantula Nebula in the Large Magellanic Cloud is the largest star yet discovered, astronomers have produced the sharpest image ever of this star.  Photo:Observatory/NOIRLab/NSF/AURA Acknowledgment

Webb’s Near-Infrared Spectrograph (NIRSpec) caught one very young star doing precisely emerging out of the dust. Astronomers previously thought this star might be a bit older and already in the process of clearing out a bubble around itself. However, NIRSpec showed that the star was only just beginning to emerge from its pillar and still maintained an insulating cloud of dust around itself. Without Webb’s high-resolution spectra at infrared wavelengths, this episode of star formation-in-action could not have been revealed.

The region takes on a different appearance when viewed in the longer infrared wavelengths detected by Webb’s Mid-infrared Instrument (MIRI). The hot stars fade, and the cooler gas and dust glow. Within the stellar nursery clouds, points of light indicate embedded protostars, still gaining mass.

While shorter wavelengths of light are absorbed or scattered by dust grains in the nebula, and therefore never reach Webb to be detected, longer mid-infrared wavelengths penetrate that dust, ultimately revealing a previously unseen cosmic environment.

Caption: NASA’s James Webb Space Telescope

One of the reasons the Tarantula Nebula is interesting to astronomers is that the nebula has a similar type of chemical composition as the gigantic star-forming regions observed at the universe’s “cosmic noon,” when the cosmos was only a few billion years old and star formation was at its peak. Star-forming regions in our Milky Way galaxy are not producing stars at the same furious rate as the Tarantula Nebula, and have a different chemical composition.

Caption: In this mosaic image displays the Tarantula Nebula star, including tens of thousands of never-before-seen young stars that were previously shrouded in cosmic dust. The most active region appears to sparkle with massive young stars, appearing pale blue./Photo:NASA

This makes the Tarantula the closest (i.e., easiest to see in detail) example of what was happening in the universe as it reached its brilliant high noon. Webb will provide astronomers the opportunity to compare and contrast observations of star formation in the Tarantula Nebula with the telescope’s deep observations of distant galaxies from the actual era of cosmic noon.

 

 

 

 

 

 

‘Seeing’ the other side of our galaxy

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Astronomers have successfully traced a spiral arm on the far side of our Galaxy, an accomplishment that provides new insights into the structure of the Milky Way. Efforts to observe the far side of our Galaxy have been hampered by the vast distance and interstellar dust that blocks optical light from those regions. Here, Alberto Sanna and colleagues used radio interferometry with the Very Long Baseline Array to trace the motions of methanol and water molecules associated with a high-mass star-forming region on the far side of the Milky Way. Using the data, they were able to locate the Scutum-Centaurus spiral arm as it passes around the far side of the Galaxy and trace the arm through almost a complete rotation. The authors note that their data suggest that the pitch angle of the spiral arm (a measure of how tight the spiral is) may vary along its length. Their observations provide a record-breaking use of parallax, the apparent motion of distant objects as the Earth orbits the Sun, to measure the distance of stars. They also verify a new method of inferring distances on the far side of our Galaxy.

Using Einstein’s Theory, Brightest Galaxy 10000 Million Light Years Away Discovered

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Using Albert Einstein’s gravitational lensing theory, scientists have discovered a galaxy at about 10,000 million light years away but thousand times brighter than the nearest Milky Way.

Anastasio Diaz-Sanches from Polytechnic University of Cartagena (UPCT) in Spain used gravitational lensing phenomenon found by Einstein to magnify the apparent image of the original object.

“Thanks to the gravitational lens” explained Sánchez, “produced by a cluster of galaxies between ourselves and the source, which acts as if it was a telescope, the galaxy appears 11 times bigger and brighter than it really is.” It appears as several images on an arc centred on the densest part of the cluster, known as ‘Einstein Ring’.

To measure it they used the Gran Telescopio Canarias at the Roque de los Muchachos Observatory in Garafía, La Palma. The advantage of this type of amplification is that it does not distort the spectral properties of the light, enabling the study of very distant objects as if they were much nearer.

The galaxy is forming stars at a rate of 1,000 solar masses per year, compared to the Milky Way which is forming stars at a rate of some twice a solar mass per year. Susana Iglesias-Groth, co-author of the research said, “This type of objects harbour the most powerful star forming regions known in the universe. The next step will be to study their molecular content”.

The research findings were published in the Astrophysical Journal Letters.

The fact that the galaxy is so bright, its light is gravitationally amplifed, and has multiple images allows us to look into its internal properties, which would otherwise not be possible with such distant galaxies.

“In the future we will be able to make more detailed studies of its star formation using interferometers such ast the Northern Extended Millimeter Array (NOEMA/IRAM),in France, and the Atacama Large Millimeter Array (ALMA), in Chile,” said IAC researcher Helmut Dannerbauer, who is another contributor to the paper.